<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>demo5</title>
</head>
<body>
  <canvas width = "300" height = "300" id = "my_Canvas"></canvas>

  <script>
     /*======= Creating a canvas =========*/

     var canvas = document.getElementById('my_Canvas');
     var gl = canvas.getContext('experimental-webgl');

     /*======= Defining and storing the geometry ======*/

     var vertices = [
        -0.7,-0.1,0,
        -0.3,0.6,0,
        -0.3,-0.3,0,
        0.2,0.6,0,
        0.3,-0.3,0,
        0.7,0.6,0 
     ]

     // Create an empty buffer object
     var vertex_buffer = gl.createBuffer();

     // Bind appropriate array buffer to it
     gl.bindBuffer(gl.ARRAY_BUFFER, vertex_buffer);
  
     // Pass the vertex data to the buffer
     gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(vertices), gl.STATIC_DRAW);

     // Unbind the buffer
     gl.bindBuffer(gl.ARRAY_BUFFER, null);

     /*=================== Shaders ====================*/

     // Vertex shader source code
     var vertCode =
        'attribute vec3 coordinates;' +
        'void main(void) {' +
           ' gl_Position = vec4(coordinates, 1.0);' +
        '}';

     // Create a vertex shader object
     var vertShader = gl.createShader(gl.VERTEX_SHADER);

     // Attach vertex shader source code
     gl.shaderSource(vertShader, vertCode);

     // Compile the vertex shader
     gl.compileShader(vertShader);

     // Fragment shader source code
     var fragCode =
        'void main(void) {' +
           'gl_FragColor = vec4(0.0, 0.0, 0.0, 0.1);' +
        '}';

     // Create fragment shader object
     var fragShader = gl.createShader(gl.FRAGMENT_SHADER);

     // Attach fragment shader source code
     gl.shaderSource(fragShader, fragCode);

     // Compile the fragmentt shader
     gl.compileShader(fragShader);

     // Create a shader program object to store
     // the combined shader program
     var shaderProgram = gl.createProgram();

     // Attach a vertex shader
     gl.attachShader(shaderProgram, vertShader);

     // Attach a fragment shader
     gl.attachShader(shaderProgram, fragShader);

     // Link both the programs
     gl.linkProgram(shaderProgram);

     // Use the combined shader program object
     gl.useProgram(shaderProgram);

     /*======= Associating shaders to buffer objects ======*/

     // Bind vertex buffer object
     gl.bindBuffer(gl.ARRAY_BUFFER, vertex_buffer);

     // Get the attribute location
     var coord = gl.getAttribLocation(shaderProgram, "coordinates");

     // Point an attribute to the currently bound VBO
     gl.vertexAttribPointer(coord, 3, gl.FLOAT, false, 0, 0);

     // Enable the attribute
     gl.enableVertexAttribArray(coord);

     /*============ Drawing the triangle =============*/

     // Clear the canvas
     gl.clearColor(0.5, 0.5, 0.5, 0.9);

     // Enable the depth test
     gl.enable(gl.DEPTH_TEST);

     // Clear the color and depth buffer
     gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);

     // Set the view port
     gl.viewport(0,0,canvas.width,canvas.height);

     // Draw the triangle
     gl.drawArrays(gl.LINES, 0, 6);

     // POINTS, LINE_STRIP, LINE_LOOP, LINES,
     // TRIANGLE_STRIP,TRIANGLE_FAN, TRIANGLES
  </script>
</body>
</html>